Output formatting basics in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of System.out.printf() in Java?

It is used to print formatted output to the console, allowing you to control how variables and text appear, such as setting decimal places or alignment.

beginner

How do you format a floating-point number to show 2 decimal places using printf?

Use %.2f in the format string. For example: System.out.printf("%.2f", 3.14159); prints 3.14.

beginner

What does the format specifier %d represent in Java's printf?

It represents a decimal integer. It is used to format integer values in the output.

intermediate

How can you align text to the right in Java's printf?

By specifying a width in the format specifier, like %10s, which right-aligns the string in a field 10 characters wide.

beginner

What is the difference between System.out.print() and System.out.println()?

print() outputs text without moving to a new line, while println() outputs text and then moves the cursor to the next line.

Which format specifier would you use to print a floating-point number with 3 decimal places?

A %s

B %.3f

C %d

D %.3d

The specifier %.3f formats a floating-point number to 3 decimal places.

What does System.out.printf("%10s", "Hi") do?

A Prints 'Hi' right-aligned in a 10-character wide space

B Prints 'Hi' left-aligned in a 10-character wide space

C Prints 'Hi' with 10 spaces after it

D Prints 'Hi' with 10 spaces before and after

The %10s specifier right-aligns the string in a field 10 characters wide.

Which method prints text and moves to a new line automatically?

A System.out.print()

B System.out.printf()

C System.out.println()

D System.out.write()

println() prints text and then moves the cursor to the next line.

How would you format an integer variable named num in printf?

A System.out.printf("%c", num);

B System.out.printf("%f", num);

C System.out.printf("%s", num);

D System.out.printf("%d", num);

%d is used to format integers in printf.

What will System.out.printf("%.1f", 2.78); output?

A 2.8

B 2.7

C 2.78

D 3.0

It rounds the number to 1 decimal place, so 2.78 becomes 2.8.

Explain how to use System.out.printf to format a number with two decimal places and right-align it in a 10-character wide field.

Think about combining width and precision in the format string.

Describe the difference between print, println, and printf in Java output.

Consider how each method handles text and line breaks.

Practice

1. Which Java method is commonly used to format output with placeholders like %d or %s?

easy

A. System.out.read

B. System.out.printf

C. System.out.println

D. System.out.print

Solution

1. Step 1: Identify formatting methods in Java

   System.out.printf and System.out.format are used for formatted output, unlike println or print which just print raw text.

2. Step 2: Recognize the method that uses placeholders

   System.out.printf uses format specifiers like %d for integers and %s for strings to format output.

3. Final Answer:

   System.out.printf -> Option B

4. Quick Check:

   Formatted output uses printf [OK]

Hint: Look for method with % placeholders for formatting [OK]

Common Mistakes:

• Confusing println with printf
• Using print which lacks formatting
• Thinking read formats output

2. Which of the following is the correct syntax to print an integer variable num with two digits padded with zeros using printf?

easy

A. System.out.printf("%02d", num);

B. System.out.printf("%2d", num);

C. System.out.printf("%d2", num);

D. System.out.printf("%d02", num);

Solution

1. Step 1: Understand zero-padding format specifier

   In printf, %02d means print an integer padded with zeros to width 2.

2. Step 2: Check each option's correctness

   %2d pads with spaces, %02d pads with zeros, %d2 and %d02 are invalid formats.

3. Final Answer:

   System.out.printf("%02d", num); -> Option A

4. Quick Check:

   Zero padding uses %0Nd [OK]

Hint: Zero pad with %0 before width number [OK]

Common Mistakes:

• Using %2d pads with spaces, not zeros
• Placing digits after %d incorrectly
• Confusing padding syntax

3. What is the output of the following Java code?

int x = 7;
System.out.printf("Value: %4d!", x);

medium

A. Value: 7!

B. Value: 7 !

C. Value: 07!

D. Value:7!

Solution

1. Step 1: Understand %4d formatting

   %4d means print integer right-aligned in a field width of 4 characters, padding with spaces on the left.

2. Step 2: Apply formatting to value 7

   7 is one digit, so 3 spaces are added before it, resulting in " 7".

3. Final Answer:

   Value: 7! -> Option A

4. Quick Check:

   Right-align integer in 4 spaces [OK]

Hint: Width number pads spaces on left for integers [OK]

Common Mistakes:

• Assuming padding is on the right
• Confusing zero padding with space padding
• Ignoring field width

4. The following code is intended to print a floating-point number with 2 decimal places:

double pi = 3.14159;
System.out.printf("%.2f", pi);

What is the error in this code?

medium

A. Missing newline character causes error.

B. %.2f is invalid format specifier for double.

C. No error; it prints 3.14 correctly.

D. Must cast pi to float before printing.

Solution

1. Step 1: Check format specifier for double

   %.2f formats floating-point numbers with 2 decimal places, valid for double type.

2. Step 2: Verify code correctness

   Code prints 3.14 without error; newline is optional and casting is unnecessary.

3. Final Answer:

   No error; it prints 3.14 correctly. -> Option C

4. Quick Check:

   %.2f formats double with 2 decimals [OK]

Hint: %.Nf formats float/double to N decimals [OK]

Common Mistakes:

• Thinking casting to float is needed
• Assuming newline is mandatory
• Believing %.2f is invalid

5. You want to print a table of names and ages aligned in columns using printf. Which format string correctly aligns the name left in 10 spaces and age right in 3 spaces?

String name = "Anna";
int age = 9;
System.out.printf("???", name, age);

hard

A. "%-3s %-10d"

B. "%10s %-3d"

C. "%10s %3d"

D. "%-10s %3d"

Solution

1. Step 1: Understand alignment flags in printf

   %-10s means left-align string in 10 spaces; %3d means right-align integer in 3 spaces.

2. Step 2: Match format to requirement

   "%-10s %3d" matches left-align name and right-align age correctly; others swap or misalign.

3. Final Answer:

   "%-10s %3d" -> Option D

4. Quick Check:

   Left-align string with - flag, right-align number default [OK]

Hint: Use %- for left-align strings, default right-align numbers [OK]

Common Mistakes:

• Swapping alignment flags
• Using wrong width numbers
• Misplacing % signs